1. Field of the Invention
The present invention relates mainly to a liquid crystal composition suitable for use in an active matrix (AM) element and an AM element comprising the composition.
2. Related Art
Classification of a liquid crystal display element based on an operating mode of liquid crystals includes phase change (PC), twisted nematic (TN), super twisted nematic (STN), electrically controlled birefringence (ECB), optically compensated bend (OCB), in-plane switching (IPS), vertical alignment (VA) and so on. Classification based on a driving mode of liquid crystals includes passive matrix (PM) and active matrix (AM). PM is classified into static, multiplex and so on and AM is classified into thin film transistor (TFT), metal insulator metal (MIM) and so on. Classification of TFT includes amorphous silicon and polycrystal silicon. The latter is classified into a high temperature type and a low temperature type according to a production process. Classification based on a light source includes a reflection type using a natural light, a transmission type using a backlight and a semi-transmission type using both.
These liquid crystal display elements comprise liquid crystal compositions having appropriate characteristics. It is necessary to improve general characteristics of the compositions in order to obtain AM elements having good general characteristics. Relation between the general characteristics of the element and those of the composition is summarized in Table 1. The general characteristics of the compositions shall be explained further based on commercially available AM elements. A temperature range of a nematic phase is related to a temperature range usable for the element. Preferably, the upper limit temperature in a nematic phase is 70xc2x0 C. or more and the lower limit temperature in a nematic phase is xe2x88x9220xc2x0 C. or less. Viscosity of the compositions is related to response time of the elements. Short response time is preferable for displaying a moving picture on the elements. Consequently, a low viscosity of the composition is preferable, and a low viscosity at low temperatures is more preferable.
Optical anisotropy of the compositions is related to a contrast ratio of the elements. A product (xcex94xc2x7d) of optical anisotropy (xcex94n) of the compositions and a cell gap (d) of the elements is designed to be approximately 0.45 xcexcm to maximize a contrast ratio. Consequently, optical anisotropy of the compositions is mainly in the range of 0.08 to 0.12. A low threshold voltage of the compositions contributes to a low power consumption and a high contrast ratio of the elements. Consequently, a low threshold voltage is preferable. A high resistivity of the compositions contributes to a high voltage holding ratio and a high contrast ratio of the elements. Consequently, the compositions having a high resistivity in the initial stage are preferable. The compositions having a high resistivity even after using for a long time are preferable.
AM-TFT elements having polycrystal silicon produced at low temperature are driven at a very large frequency in comparison with AM-TFT elements having amorphous silicon. Accordingly, for the former elements, the compositions in which dielectric anisotropy has a low frequency dependence are preferable. The compositions having a low frequency dependence at low temperatures are more preferable. Especially desired are liquid crystal compositions which are also usable in the AM-TFT elements having polycrystal silicon produced at low temperatures. Related compositions hitherto known are disclosed in the following patents; JP 2-233626 A (1990) (EP 1179522 A), JP 8-73856 A (1996), JP 8-73857 A (1996), JP 10-204436 A (1998), JP 10-231482 A (1998), JP 10-298127 A (1998), JP 2000-144135 A (2000), JP 2001-3053 A (2001), JP 2001-123170 A (2001), JP 2001-288470 A (2001), JP 2001-335586 A (2001), JP 2001-342195 A (2001), and JP 2002-20344 A (2002).
The present invention comprises the following A and B.
A. A liquid crystal composition comprising; as a first component, at least one compound selected from a group of compounds represented by Formula (1); as a second component, at least one compound selected from a group of compounds represented by Formula (2); as a third component, at least one compound selected from a group of compounds represented by Formula (3); as a forth component, at least one compound selected from a group of compounds represented by Formula (4); and as a fifth component, at least one compound selected from a group of compounds represented by Formulas (5-1) and (5-2). 
wherein R1 is alkyl; R2 is alkyl or alkenyl; R3 is alkyl, alkoxy, or xe2x80x94CF3; R4 is alkyl or alkoxy; R5 is alkyl or alkoxymethyl; A1 is 1,4-cyclohexylene or 1,4-phenylene in which any hydrogen may be replaced by fluorine; A2 is 1,4-cyclohexylene or 1,4-phenylene; Z1 is a single bond or xe2x80x94COOxe2x80x94; and X1 is hydrogen or fluorine.
B. A liquid crystal display element comprising the liquid crystal composition described above.
An object of the present invention is to provide a liquid crystal composition which satisfies plural characteristics in the general characteristics of a composition, a low threshold voltage, a high resistivity, and a low frequency dependence. Low frequency dependence means that frequency dependence of dielectric anisotropy is low. Another object is to provide a liquid crystal composition having plural characteristics appropriately balanced. A further object is to provide a liquid crystal display element comprising the composition and especially having a high voltage holding ratio. A still further object is to provide an AM-TFT element having polycrystal silicon produced at low temperatures.
The present invention comprises the following items 1 to 20.
1. A liquid crystal composition comprising; as a first component, at least one compound selected from a group of compounds represented by Formula (1); as a second component, at least one compound selected from a group of compounds represented by Formula (2); as a third component, at least one compound selected from a group of compounds represented by Formula (3); as a forth component, at least one compound selected from a group of compounds represented by Formula (4); and as a fifth component, at least one compound selected from a group of compounds represented by Formulas (5-1) and (5-2). 
xe2x80x83wherein R1 is alkyl; R2 is alkyl or alkenyl; R3 is alkyl, alkoxy, or xe2x80x94CF3; R4 is alkyl or alkoxy; R5 is alkyl or alkoxymethyl; A1 is 1,4-cyclohexylene or 1,4-phenylene in which any hydrogen may be replaced by fluorine; A2 is 1,4-cyclohexylene or 1,4-phenylene; Z1 is a single bond or xe2x80x94COOxe2x80x94; and X1 is hydrogen or fluorine.
2. The liquid crystal composition as described in the above item 1, wherein the fifth component is at least one compound selected from a group of compounds represented by Formula (5-1).
3. The liquid crystal composition as described in the above item 1, wherein the fifth component is at least one compound selected from a group of compounds represented by Formula (5-2).
4. The liquid crystal composition as described in the above item 1, wherein the first component is in the range of 5 to 30% by weight, the second component is in the range of 10 to 40% by weight, the third component is in the range of 10 to 50% by weight, the forth component is in the range of 3 to 30% by weight, and the fifth component is in the range of 3 to 40% by weight, each based on the total weight of the composition.
5. The liquid crystal composition as described in the above item 2, wherein the first component is in the range of 5 to 30% by weight, the second component is in the range of 10 to 40% by weight, the third component is in the range of 10 to 50% by weight, the forth component is in the range of 3 to 30% by weight, and the fifth component is in the range of 3 to 40% by weight, each based on the total weight of the composition.
6. The liquid crystal composition as described in the above item 3, wherein the first component is in the range of 5 to 30% by weight, the second component is in the range of 10 to 40% by weight, the third component is in the range of 10 to 50% by weight, the forth component is in the range of 3 to 30% by weight, and the fifth component is in the range of 3 to 40% by weight, each based on the total weight of the composition.
7. The liquid crystal composition as described in the above item 1, further comprising, as a sixth component, at least one compound selected from a group of compounds represented by Formula (6). 
xe2x80x83wherein R1 is alkyl; X1 and X2 independently are hydrogen or fluorine; and n is 0 or 1.
8. The liquid crystal composition as described in the above item 2, further comprising, as a sixth component, at least one compound selected from a group of compounds represented by Formula (6). 
xe2x80x83wherein R1 is alkyl; X1 and X2 independently are hydrogen or fluorine; and n is 0 or 1.
9. The liquid crystal composition as described in the above item 3, further comprising, as a sixth component, at least one compound selected from a group of compounds represented by Formula (6). 
xe2x80x83wherein R1 is alkyl; X1 and X2 independently are hydrogen or fluorine; and n is 0 or 1.
10. The liquid crystal composition as described in the above item 4, further comprising, as a sixth component, at least one compound selected from a group of compounds represented by Formula (6). 
xe2x80x83wherein R1 is alkyl; X1 and X2 independently are hydrogen or fluorine; and n is 0 or 1.
11. The liquid crystal composition as described in the above item 5, further comprising, as a sixth component, at least one compound selected from a group of compounds represented by Formula (6). 
xe2x80x83wherein R1 is alkyl; X1 and X2 independently are hydrogen or fluorine; and n is 0 or 1.
12. The liquid crystal composition as described in the above item 6, further comprising, as a sixth component, at least one compound selected from a group of compounds represented by Formula (6). 
xe2x80x83wherein R1 is alkyl; X1 and X2 independently are hydrogen or fluorine; and n is 0 or 1.
13. The liquid crystal composition as described in the above item 7, wherein the sixth component is in the range of 1 to 40% by weight based on the total weight of the composition.
14. The liquid crystal composition as described in the above item 8, wherein the sixth component is in the range of 1 to 40% by weight based on the total weight of the composition.
15. The liquid crystal composition as described in the above item 9, wherein the sixth component is in the range of 1 to 40% by weight based on the total weight of the composition.
16. The liquid crystal composition as described in the above item 10, wherein the sixth component is in the range of 1 to 40% by weight based on the total weight of the composition.
17. The liquid crystal composition as described in the above item 11, wherein the sixth component is in the range of 1 to 40% by weight based on the total weight of the composition.
18. The liquid crystal composition as described in the above item 12, wherein the sixth component is in the range of 1 to 40% by weight based on the total weight of the composition.
19. A liquid crystal display element comprising the liquid crystal composition as described in any one of the above items 1 to 18.
20. The liquid crystal display element as described in the above item 19, wherein the liquid crystal display element is an AM element.
Technical terms used herein have the following meanings. The liquid crystal composition(s) or liquid crystal display element(s) of the present invention may be abbreviated to xe2x80x9cthe composition(s)xe2x80x9d or xe2x80x9cthe element(s)xe2x80x9d, respectively. A liquid crystal display element(s) is a generic term for a liquid crystal display panel(s) and a liquid crystal display module(s). A main component of a liquid crystal composition is a liquid crystal compound(s). The liquid crystal compound is a generic term for a compound having a liquid crystal phase such as a nematic phase, a smectic phase and so on, and a compound having no liquid crystal phase, but useful as a component of the composition. At least one compound selected from a group of compounds represented by Formula (1) may be abbreviated to xe2x80x9ccompound (1)xe2x80x9d. Compounds represented by any other formulas may be abbreviated in a similar manner.
The upper limit temperature of a nematic phase may be abbreviated to xe2x80x9cupper limit temperaturexe2x80x9d. The lower limit temperature of a nematic phase may be abbreviated to xe2x80x9clower limit temperaturexe2x80x9d. xe2x80x9cHigh resistivityxe2x80x9d means that the composition has a high resistivity in the initial stage and even after using over a long period of time. xe2x80x9cHigh voltage holding ratioxe2x80x9d means that an element has a high voltage holding ratio in the initial stage and even after using over a long period of time. Characteristics such as optical anisotropy are explained using the values measured according to the respective methods written in the Examples. A component ratio (percentage) in a composition is in terms of weight percentage (% by weight) based on the total weight of the composition.
In the chemical formulas of the compounds as a component, symbol R1 is used for plural compounds. In these compounds, R1 may have the same or different meaning. In one case, for example, R1 of the compound (1) is ethyl and R1 of the compound (2) is ethyl. In another case, R1 of the compound (1) is ethyl and R1 of the compound (2) is propyl. This rule is also applied to symbols R2, R3, R4, R5, R6, A1, A2, X1, and X2.
The compositions of the present invention satisfy plural characteristics in the general characteristics of a composition, a low threshold voltage, a high resistivity, and a low frequency dependence. xe2x80x9cLow frequency dependencexe2x80x9d means that frequency dependence of the dielectric anisotropy is low. The compositions have plural characteristics that are appropriately balanced. The elements comprising the compositions have an especially large voltage holding ratio. The compositions are especially suitable for an AM-TFT element having polycrystal silicon produced at low temperatures.
The compositions of the present invention shall be explained in the following order: Firstly, constitution of components in the present compositions; secondly, main characteristics of component compounds and their main effects on the composition; thirdly, a preferred ratio of component compounds and reasons therefor; fourthly, preferred embodiments of component compounds; fifthly, concrete examples of component compounds; and sixthly, a method for the preparation of a component compound.
Firstly, constitution of components in the present compositions is explained. There are six types of combination of component compounds. Types 1 to 6 are summarized in Table 2, wherein the component compounds in each of types 1 to 6 are indicated by the symbol of a circle. A blank column denotes that no corresponding compound is used as a component. In type 1, for example, compounds (1), (2), (3), (4), (5-1), and (5-2) are the components of the composition.
The compositions of the present invention are classified into Composition A and Composition B. Composition A may further comprise other compounds different from compounds (1) to (6), such as a liquid crystal compound, an additive, and so on. The liquid crystal compound is mixed into the composition for the purpose of adjusting the characteristics. The additive is an optically active compound, a coloring matter, and so on. The optically active compound is mixed into the composition for the purpose of inducing a helical structure of liquid crystals to give a twist angle. The coloring matter is mixed into the composition to make it applicable to an element of GH (Guest host) mode.
Composition B consists essentially of compounds selected from the compounds (1) to (6). The term xe2x80x9cessentiallyxe2x80x9d here means that the composition contains no liquid crystal compound which is different from these compounds. The term also means that the composition may further comprise compounds such as impurities contained in these compounds, an optically active compound, a coloring matter, and so on. The number of components in Composition B is smaller than that in Composition A. Composition B is more preferable to Composition A in terms of cost. On the other hand, Composition A is preferable to Composition B in that the physical properties of Composition A can be adjusted further by mixing other liquid crystal compounds.
Secondly, main characteristics of component compounds and their main effects on the composition are explained. Main characteristics of the compounds are summarized in Table 3, wherein xe2x80x9cLxe2x80x9d means large or high, xe2x80x9cMxe2x80x9d means middle, and xe2x80x9csxe2x80x9d means small or low. xe2x80x9c0xe2x80x9d means that the dielectric anisotropy is nearly zero (or extremely small). Symbols xe2x80x9cLxe2x80x9d, xe2x80x9cMxe2x80x9d and xe2x80x9cSxe2x80x9d are based on relative evaluation of these compounds.
Compounds (1) to (6) increase resistivity of the composition. A compound having a high upper limit temperature elevates the upper limit temperature of the composition. A compound having a low viscosity decreases the viscosity of the composition. A compound having a small optical anisotropy decreases the optical anisotropy of the composition. A compound having a large dielectric anisotropy decreases the threshold voltage of the composition. A compound having a low frequency dependence of dielectric anisotropy decreases the frequency dependence of dielectric anisotropy of the composition.
Thirdly, preferred ratios of component compounds and the reasons therefor are explained. A preferred ratio of compound (1) is 5% or more for reducing the threshold voltage or decreasing the frequency dependence of the composition and 30% or less for reducing the lower limit temperature of the composition. A more preferred ratio is 5 to 20%. A preferred ratio of compound (2) is 10% or more for reducing the threshold voltage of the composition and 40% or less for reducing the lower limit temperature of the composition. A more preferred ratio is 15 to 30%. A preferred ratio of compound (3) is 10% or more for decreasing the viscosity or adjusting the threshold voltage of the composition and 50% or less for reducing the lower limit temperature of the composition. A more preferred ratio is 15 to 40%.
A preferred ratio of compound (4) is 3% or more for decreasing the viscosity of the composition and 30% or less for reducing the lower limit temperature of the composition. A more preferred ratio is 5 to 20%. A preferred ratio of compound (5-1) or (5-2) is 3% or more for elevating the upper limit temperature of the composition and 40% or less for reducing the lower limit temperature of the composition. A more preferred ratio is 5 to 25%. Compound (6) is mixed into the composition for further adjusting the threshold voltage and upper limit temperature. A preferred ratio of this compound is 1% or more for adjusting the characteristics of the composition and 40% or less for reducing the lower limit temperature of the composition. A more preferred ratio is 1 to 35%.
Fourthly, preferred embodiment of a component compound are explained. Preferred R1 is alkyl having 1 to 10 carbons. Preferred R2 is alkyl having 1 to 10 carbons or alkenyl having 2 to 10 carbons. Preferred R3 is alkyl having 1 to 10 carbons, alkoxy having 1 to 10 carbons or xe2x80x94CF3. Preferred R4 is alkyl having 1 to 10 carbons or alkoxy having 1 to 10 carbons. Preferred R5 is alkyl having 1 to 10 carbons or alkoxymethyl having 1 to 10 carbons. Preferred R6 is alkyl having 1 to 10 carbons.
Preferred alkyl is methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, or octyl. More preferable is ethyl, propyl, butyl, pentyl, or heptyl.
Preferred alkenyl is vinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, or 5-hexenyl. More preferable is vinyl, 1-propenyl, 3-butenyl, or 3-pentenyl. A preferred configuration of xe2x80x94CHxe2x95x90CHxe2x80x94 in these alkenyl groups depends on the position of the double bond. In the alkenyl such as 1-propenyl, 1-butenyl, 1-pentenyl, 1-hexenyl, 3-pentenyl and 3-hexenyl, trans configuration is preferable. In the alkenyl such as 2-butenyl, 2-pentenyl and 2-hexenyl, cis configuration is preferable.
Preferred alkoxy is methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, or heptyloxy. More preferable is methoxy or ethoxy.
Preferred alkoxymethyl is methoxymethyl, ethoxymethyl, propoxymethyl, butoxymethyl, or pentyloxymethyl. More preferable is methoxymethyl.
xe2x80x9c1,4-Phenylene in which any hydrogen may be replaced by fluorinexe2x80x9d for A1 is 1,4-phenylene, 2-fluoro-1,4-phenylene, 2,5-difluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene, 2,3,5-trifluoro-1,4-phenylene, or 2,3,5,6-tetrafluoro-1,4-phenylene. Among these groups, 1,4-phenylene, 2-fluoro-1,4-phenylene, 2,5-difluoro-1,4-phenylene, or 2,6-difluoro-1,4-phenylene is preferable. More preferable is 1,4-phenylene, 2-fluoro-1,4-phenylene, or 2,6-difluoro-1,4-phenylene. The group 1,4-cyclohexylene or 1,3-dioxane-2,5-diyl of the component compounds is preferably in trans configuration than cis configuration.
Fifthly, concrete examples of the component compounds are given. Preferred compounds (1) and (3) to (6) are shown below as compounds (1-1) to (1-2), (3-1) to (3-6), (4-1) to (4-5), (5-1-1) to (5-2-5) and (6-1) to (6-3). No example of compound (2) is given here. R1 and R6 are independently alkyl, and R2 is alkyl or alkenyl. 
Sixthly, the method for the preparation of the compounds as a component is explained. These compounds can be prepared by known methods as specified below. Compound (1-1) is prepared according to the method disclosed in JP 59-170042 A (1984). Compounds (1-2) and (2) are prepared according to the method described in JP 2-233626 A (1990). Compound (3-1) is prepared according to the method described in JP 57-154135 A (1982). Compound (3-3) is prepared according to the method described in JP 57-185230 A (1982). Compound (4-1) is prepared according to the method described in JP 59-70624 (1984). Compound (4-4) is prepared according to the method described in JP 56-68636 A (1981). Compound (5-1-2) and (5-1-3) are prepared according to the method described in JP 57-165328 A (1982). Compound (5-2-3) is prepared according to the method described in JP 58-219137 A (1983). Compound (5-2-5) is prepared according to the method described in JP 2-237949 A (1990). Compound (6-1) is prepared according to the method described in JP 57-64645 A (1982).
The compounds for which preparation methods are not specified above can be prepared according to the methods described in books such as Organic Syntheses (John Wiley and Sons, Inc.), Organic Reactions (John Wiley and Sons, Inc.), Comprehensive Organic Synthesis (Pergamon Press), New Experimental Chemistry Course (Shin Jikken Kagaku Kouza) (Maruzen, Inc.), and so on. The composition is prepared from the compounds thus obtained according to known methods. For example, the component compounds are mixed and heated to dissolve each other to give the composition.
The optical anisotropy of the present composition mainly ranges from 0.07 to 0.14. The composition having the optical anisotropy of 0.07 to 0.18 or 0.06 to 0.20 may be prepared by controlling the mixing ratio of the component compounds or by further mixing any liquid crystal compounds other than the component compounds. An element comprising the composition has a high voltage holding ratio. Accordingly, the composition of the present invention is suitable for an AM element. The composition is especially suitable for an AM-TFT element having polycrystal silicon prepared at low temperatures, because its frequency dependence of the dielectric anisotropy is low. The composition can be used not only for an AM element but also for a PM element. The composition can be used for elements having modes such as PC, TN, STN, ECB, OCB, IPS, VA, and so on. These elements may be reflection type, transmission type or semi-transmission type elements. The composition can also be used for such elements as a nematic curvilinear aligned phase (NCAP) element prepared by microcapsulating the composition and a polymer dispersed (PD) element comprising the composition in which a three-dimensional reticulated polymer is formed, e.g., a polymer network (PN) element.